1. Field of the Invention
This invention relates to Hall effect apparatus and more particularly to flux concentrator assembly means for Hall effect apparatus.
2. Description of the Prior Art
U.S. Pat. No. 3,825,777 entitled "Hall Cell with Offset Voltage Control", R. J. Braun and assigned to the common assignee herein, contains a general description of Hall effect devices. Briefly, as described therein, a Hall effect device generally comprises a body of Hall material. A transverse electric field is created in the body by the passage of current through the body between two spaced electrodes across which is connected an appropriate electrical supply. The two electrodes are referred to synonymously in the art, and as used herein, as the input, main, control and/or current electrodes. A second pair of spaced electrodes are located intermediate of the current electrodes. The second pair of electrodes are referred to synonymously in the art, and as used herein, as the output, sense, sensor, sensing probe, or Hall electrodes. In the semiconductor Hall cell types, the body is in addition a semiconductor material of a given conductivity type and the electrodes are generally co-planar.
In operation, the body is inserted in a magnetic field which is or has a component normal to the plane formed by the intersection of the current passing through the body and the resultant transverse electrical field it produces. Under these conditions, a Hall voltage results between the sense electrodes. This Hall voltage is proportional to the main current and magnetic field strength. The voltage across the sense electrodes will be at a null whenever the magnetic field is absent and/or the main current is absent. Ideally, if the two sense electrodes are apatially located on an equipotential line or points of the electric field, the null voltage will be zero. However, in practice because of factors due to magnetic remanescence, manufacturing tolerances and the like and/or as well as external conditions such as changes in environmental parameters as temperature and the like, the null is generally at some other finite level. The null voltage is referred to as an offset voltage.
In the aforementioned U.S. Pat. No. 3,825,777, the Hall devices described therein are in particular provided with offset voltage controls which include one or more auxiliary electrodes disposed at preselected spatial positions of the Hall device body between its current and sense electrodes. The auxiliary electrode(s) when connected to a predetermined electrical supply provide an auxiliary electrical field that controls the offset voltage at the sense electrodes.
It is also well known to those skilled in the art that the magnetic field sensitivity of a Hall device varies inversely with the magnetic reluctance of the total flux path. U.S. Pat. No. 3,845,445 entitled "Modular Hall Effect Device", R. J. Braun et al and assigned to the common assignee herein, describes an arrangement of two flux concentrators with an effective magnetic air gap therebetween. The gap is only slightly more than the thickness of the Hall device located in the gap and there results an improved sensitivity.
Referring more specifically and in greater detail to the flux concentrator arrangement and Hall device of the aforementioned U.S. Pat. No. 3,845,445, the two concentrators are bascially a soft iron carrier plate and a T-shaped soft iron flux concentrator, respectively, and the Hall device is a semiconductor chip, i.e. planar, type, with the electrodes thereof located on one of its planar surfaces, hereinafter sometimes referred to as its electrode surface.
The two flux concentrators and chip are part of a module, which is of the pluggable type. The module includes a box-like molded plastic housing. The housing has two juxtaposed mating sections, to wit: a rectangular-shaped base section and a compatible rectangular-shaped top section. The last mentioned section has an inner rectangular cavity that is in facing relationship with the topside of the base section in a cover-like manner. In the final assembly, the two sections are joined together by ultrasonic welding or other suitable means.
The top, i.e. upper, section of the housing has a central rectangular opening which extends from the top, i.e. outer, surface of the upper section to the aforementioned inner cavity. The T-shaped flux concentrator is mounted in this opening as an insert with the sidewalls of its compatibly contoured rectangular-shaped horizontal cross arm portion in direct contact with the sidewalls of the hole and such that its vertical leg portion extends freely and fully into the aforementioned cavity. The top surface of the T-shaped flux concentrator is flush with the top surface of the top section.
In the base section, a central rectangular hole extends from the topside of the base section to an elongated groove which runs along the underside of the base section. The groove has a U-shaped channel-like configuration with a rectangular cross-section and extends partially inward from the aforementioned underside. The groove is in colinear alignment with one of the central orthogonal longitudinal axes of the rectangular base section. The central rectangular hole of the base section and the rectangular flux concentrator carrier plate have compatible dimensions so that the plate is mounted as an insert in the hole, their respective adjacent sidewalls being in direct contact with each other. The plate is located at the lower end of the hole with the lower surface of the carrier plate being flush with the surface of the horizontal or base portion of the channel.
As such, the carrier plate has its lower side, i.e. surface, seated on the top surface of a band or strap-like soft iron flux core concentrator, which is mounted as an insert in the groove. The strap-like concentrator has a rectangular cross-section configuration compatible to that of the groove. As a result, the walls of the groove are in direct contact with the adjacent surfaces of the strap-like concentrator, and the latter's bottom surface is flush with the underside of the base section. The Hall effect chip, which is smaller than the carrier, has its non-electrode planar surface in turn bonded directly to the upper side of the carrier plate by an epoxy. The chip is thus located partially in the central hole of the housing's base section and extends upwardly and outwardly into the cavity of the housing's top section with the electrode planar surface of the chip being above the plane of the topside of the base section. Four flying leads, i.e. wire conductors, connect the four electrodes of the Hall chip to the heads of four pluggable terminal pins, respectively, of the module.
The four pins are mounted in the housing base section in a symmetrical manner, two on each side of the groove and are normal to the base section's topside and underside parallel planar surfaces. More specifically, the heads of the pins extend slightly above the top surface of the base section and into the cavity of the top section, and the lower ends of the pins extend outwardly from the underside of the bottom section an appropriate uniform distance so as to effectuate a pluggable module configuration.
The T-shaped concentrator mounted in the top section is in alignment with the chip and carrier plate mounted in the base section, when the two sections are in final assembly. In some cases, the carrier plate may be obviated and in which case the chip is directly bonded to the top of the flux concentrator strap where it is exposed through the central hole in the base section.
The flux concentrator strap for most of the embodiments described in U.S. Pat. No. 3,845,445 is U-shaped with the longitudinal base portion thereof being flush mounted in the groove as aforementioned and each of the two vertical legs thereof being extended upwards from the groove through appropriately aligned holes in the base and top sections of the housing. Each leg and the aligned holes through which it extends are compatibly contoured placing their respective adjacent surfaces in direct contact.
In the housing top section, the two holes provided for each strap leg symmetrically straddle and are in linear alignment with the aforementioned central opening provided for the T-shaped flux concentrator member. The top section's two holes, which are provided for the legs, extend from the topside of the top section and through two opposite sidewalls thereof which form two of the sides of the aforementioned cavity. Each of the top section's two holes extend to the respective aligned corresponding one of the two holes of the base section provided for each strap leg.
The last mentioned two holes of the base section symmetrically straddle and are in linear alignment with the aforementioned central hole of the base section provided for the carrier plate and Hall effect chip. The two strap leg holes of the base section extend from the topside of and down through the base section to the horizontal portion of the aforementioned U-shaped groove formed on the underside of the base section.
In one embodiment, the end faces of the both legs of the flux concentrator strap are flush with the top surface of the top section. In another embodiment, only the end face of one leg is flush with the top surface of the top section, the other leg being further extended above the top surface and formed into a loop which places its end face in contact with the top of the flush mounted T-shaped concentrator, and to which it is then directly connected.
In still another embodiment, the legs of the flux concentrator strap are removed and only the base portion of the strap is mounted in the groove. One leg of an external U-shaped soft iron member is directly connected to the underside of the flush mounted base portion of the flux concentrator strap in the base section and the other leg is directly connected to the top of the flush mounted T-shaped flux concentrator in the top section.
The Hall effect modules or packages of U.S. Pat. No. 3,845,445, while permitting close tolerance positioning of the flux concentrators to the chip Hall area, were not conducive to precision mounting of the flux concentrators in a simple and/or reliable manner. As a result, the air gap, i.e. spacing, between the two flux concentrators in which the chip is located was capable of varying from module to module of the same nominal size and thereby adversely effecting the standardization and/or calibration of the module.
Moreover, the aforedescribed modules of U.S. Pat. No. 3,845,445 were not readily conducive to assembly and/or disassembly. For example, by ultrasonically welding the top and bottom housing sections together, the chip and flying lead connections thereof were not accessible for replacement and/or repair without destruction of one or both of the sections and hence the module per se. Also, because the flux concentrator inserts were flush mounted with the respective surfaces of the housing sections, accessibility for direct connection thereto was limited and/or unreliable, particularly in those cases where an external loop type soft iron member was to be directly connected thereto. Moreover, these loop type members were not readily disconnectable from the flux concentrators. Thus, for example, the attachment or detachment of the loop member around an external wire conductor, in the case of the use of the module as a current sensor, was not facilitated by the aforedescribed modules. Thus, for example, the wire conductor to be sensed had to be severed or disconnected at one end to allow passage of the wire conductor through the loop-like member which is impractical and/or undesirable in many applications.